DE69915851T2 - OPTICAL SENSOR WITH STACKED DIELECTRIC LAYERS - Google Patents

Description

Territory of invention

The The present invention relates generally to the field of optical Investigation and in particular an optical sensor with a dielectric Film stack.

background the invention

Extreme sensitive optical sensors are made by exploiting an effect as surface plasmon resonance (SPR) is constructed. These sensors are able to the presence of a variety of materials in concentrations of Picomol per liter. SPR sensors are for detection numerous biomolecules, including Keyhole limpet hemocyanin, α-fetoprotein, IgE, IgG, bovine and human serum albumin, glucose, urea, avidin, Lecithin, DNA, RNA, HIV antibodies, Human transferrin and chymotrypsinogen. Furthermore, SPR sensors are built been the chemicals such. As polyazulen and nitrobenzene and different gases, such as. Halothane, trichloroethane and carbon tetrachloride detect.

One SPR sensor is made by sensitizing a surface of a Substrate opposite a specific substance. Typically, that is surface the substrate with a thin metal foil, such as B, made of silver, gold or aluminum, coated. Next will be a monomolecular layer of Sensibilisiermaterial such. B. a complementary antigen, covalent with the surface of the thin Foil bonded. In this way, the thin film is able to with a predetermined chemical, biochemical or biological Substance to interact. When a SPR sensor is exposed to a sample that contains a target substance connects the substrate with the Sensibilisiermaterial and changed the effective refractive index at the surface of the sensor. Detecting the target substance is made by observing the optical properties the surface of the SPR sensor.

There are two common versions of an SPR sensor. 1 shows a prism-based SPR sensor 10 , which is the most common form of SPR sensor. The sensor 10 has a disposable slide 20 on top of a solid glass prism 12 is placed. The slide 20 is with a metal foil 16 coated, and the Sensibilisiermaterial 22 is able to substance with the target 18 in the sample 21 to interact. Before placing the slide 20 on the prism 12 An operator coats the prism 12 with an antireflection coating 14 , which is often a fluid, to prevent a light beam 24 is reflected before the metal foil layer 16 reached.

A light source 28 generates the light beam 24 that's on the sensor 10 incident. The sensor 10 reflects the light beam 24 as a ray of light 26 that of a detector 30 Will be received. At a specific angle of incidence of the light beam 24 , which is known as the resonance angle, carried out a very efficient energy transfer and a very efficient excitation of the surface plasmon in the metal foil 16 , Consequently, the reflected light shows 26 an anomaly, such as As a strong damping, and the resonance angle of the sensor 10 easily detected. If the target substance 18 with the sensitizing material 22 connects, there is a shift of the resonance angle due to the change in the refractive index at the surface of the sensor 10 , A quantitative measure of the concentration of the target substance 18 can be calculated by the magnitude of the shift of the resonance angle.

A second common embodiment of an SPR sensor, known as a diffraction grating-based SPR sensor, involves the use of a metal diffraction grating instead of a glass prism. 2 shows a diffraction grating based SPR sensor 40 in which a substrate 45 is formed such that it has sinusoidal grooves. In diffraction grating-based SPR sensors, the period of the groove profile of the substrate is 45 typically between 0.4 μm and 2.0 μm. A thin metal foil 42 is outside the surface of the substrate 45 applied and has a suitable metal, such as. As aluminum, gold or silver. In one embodiment, the layer 42 Silver with a thickness of about 100 nm.

A sensitizing layer 44 is outside the metal foil 42 applied. The sensitizing layer 44 is chosen to be with a predetermined chemical, biochemical or biological substance 18 in a sample 21 interacts. In one embodiment, the sensitizing layer 44 an antigenic layer capable of trapping a complementary antibody. Recently, there have been several techniques for linking antigens as receptors with the film 42 been developed, such. As the spin-coating with a porous silica sol-gel or hydrogel matrix. Preferably, the sensitizing layer has 44 a thickness of less than 100 nm.

In 2 creates the light source 28 the light beam 24 that on the sensor 40 that hits the detector 30 the reflected light beam 26 receives. In a diffraction grating based SPR sensors resonates and shows the reflected light beam 26 an anomaly when a polarization component of the light beam 24 orthogonal to the groove direction of the surface of the substrate 45 runs and the angle of incidence of the light beam 24 for energy transfer and excitation of the surface plasmon in the thin metal foil 42 suitable is.

On diffraction grating based SPR sensors have several unique ones Advantages over prism-based SPR sensors. For example, the Resonance angle of a diffraction grating based SPR sensors Fine tuned by adjusting the groove profile. Further is no antireflection coating on SPR sensors based on a diffraction grating required. Grit-based SPR sensors are However disadvantageous in that, in contrast to on a Prism-based sensors that affect the incident light propagated through the prism and on the opposite of the sample Metal foil impinges, which must propagate light through the sample. The Propagating through the sample is disadvantageous because the sample tends to to absorb or scatter the incident light. From these establish are diffraction-grating-based SPR sensors for testing of liquids, such as As blood, bad and are primarily on the Area of gas detection used. Further, both are described above SPR sensors on a highly conductive metal foil to support the Surface plasmon resonance reliant. However, this metal foil limits the wavelength of the Resonance on the red or infrared region of the light spectrum, since at shorter wavelength the conductivity itself the best metals are not enough to produce strong resonances, which leads to a lower sensitivity.

In WO-A-90/08318 is a biosensor with a dielectric resonant cavity described limited by a multilayer dielectric stack is, which acts as a dielectric mirror. As a dielectric Mirror, the dielectric stack provides a nearly complete inner Reflection about a wide range of angles to prevent light from coming out emerges from the resonant cavity.

In EP-A-0 175 585 describes a dielectric film stack, which forms the sheath of a hollow fiber core.

Out the above and other reasons listed below, the for professionals in the art in reading the present invention There is a need in the art for an optical sensor with the advantages of a diffraction grating-based SPR sensor, which does not require that the incident light propagated through the sample.

Summary overview of the invention

It discloses a method and apparatus for optical inspection a target substance in a sample using a sensor according to claim 1, 2 and 10, respectively, with which the above-described defects, the at conventional on a diffraction grating and prism-based SPR sensors occur, be eliminated.

Of the inventive sensor shows a strong resonance comparable in size to the resonances is the conventional one Normally have SPR sensors. Unlike when on a diffraction grating based SPR sensors However, a sample can be obtained by reflection from the substrate side without Reproduction of light through the sample can be studied. Further allows the sensor examining a sample with transmitted light. An advantage The examination with transmitted light lies in the possibility of being a source of diffused To use light. Because the sensor does not rely on the use of conductive metals instructed allows the sensor has strong resonances at shorter wavelengths than it at conventional SPR sensors is the case.

According to one Aspect, the invention relates to a sensor with a dielectric Film stack with multiple dielectric layers. The dielectric Layers act as waveguides, so that is part of the incident light in at least one angle of incidence in the dielectric Film pile propagates. In one embodiment, the dielectric Layers made of a dielectric material that either of a first dielectric material having a first refractive angle or a second dielectric material having a second refractive angle selected is. In one configuration, the dielectric film stack is such formed such that the dielectric material of the dielectric Layers between the first dielectric material and the second dielectric material alternated. The dielectric film stack can be designed as a dielectric mirror, so that the sensor incident light is substantially reflected by the sensor, or be designed as an antireflection film stack, so that incident Light transmitted substantially unreflected by the sensor becomes.

In another aspect, the invention relates to a scanning system having a sensor with a stack of dielectric layers. A light source exposes the sensor to a light beam. The dielectric layers act as waveguides, so that a portion of the incident light propagates in at least one incident angle in the dielectric film stack. A detector receives light from the sensor and generates an output signal that represents the strength of the received light. A controller is coupled to the detector and calculates a measure of the substance in the sample as a function of the output signal. In one embodiment, a diffuser produces the incident diffused light beam from the light source and a lens focuses the light transmitted through a passage angle through the sensor onto a corresponding element of the detector array.

According to one In another aspect, the invention relates to a method for testing a target substance in a sample. A sensor interacts with the a target substance containing sample. The sensor has a dielectric Film stack with several dielectric layers on, as Waveguide for act incident light. A measure of the target substance in the Sample will depend on a shift of a detected optical anomaly from determines the light coming from the sensor. In one embodiment the measure gets through Detecting an optical anomaly in reflected from the sensor Light determines. In a further embodiment, the measure comprises detecting an optical anomaly in light transmitted through the sensor.

These and other features and advantages of the invention will be apparent from the following detailed description of the preferred embodiments of Invention obvious.

Short description the drawings

1 shows a schematic side view of a scanning system with a prism based surface plasmon resonance sensor;

2 shows a schematic side view of a scanning system with a diffraction grating-based Oberflächenplamsonresonanz- sensor;

3 shows a cross section of an embodiment of an optical sensor according to the invention with a dielectric film stack; and

4 FIG. 12 shows a schematic side view of an embodiment of a scanning system for examining a substance in a sample by exposing a sensor comprising a dielectric film stack and detecting a displacement at one or more resonance angles.

detailed description

In The following detailed description is attached to the attached Referring to the drawings, the specific embodiments of the invention demonstrate. It can electrical, mechanical and structural changes to the embodiments without prejudice to the scope of the present Deviated from the invention. The following detailed description should not be considered as a restriction and the scope of the present invention defined by the appended claims.

3 shows a cross-sectional profile of an optical sensor according to the invention 50 , It has been found that an optical sensor can be constructed which has resonance angles comparable to those of conventional SPR sensors, but with which many of the disadvantages described above can be eliminated. In particular, in the sensor 50 used a dielectric film stack instead of a thin metal foil. The sensor 50 has a substrate 51 with a surface 53 , are formed in the sinusoidal grooves on. The period of the groove profile of the surface 53 can be between less than 0.4 μm and more than 2.0 μm. Other groove profiles, such. B. trapezoidal, square, etc., are also suitable for the invention.

Outside the area 53 of the substrate 51 are several transparent dielectric layers 52 formed, which together a dielectric film stack on the surface 53 of the substrate 51 form. Although illustrated in this way, the dielectric layers need 52 not the surface profile of the substrate 51 to be adapted. As explained in more detail below, the sensor shows 50 strong resonances that are comparable in size to the resonances that normally occur with SPR sensors. In one embodiment, the dielectric layers are 52 of the dielectric film stack is configured to act as a dielectric mirror, which at substantially non-resonant angles substantially the entire light beam 62 Reflected. In particular, each dielectric layer reflects 52 of the dielectric film stack a part of the light beam 62 as a ray of light 66 , This embodiment is advantageous in that, unlike SPR sensors based on a diffraction grating, the sample 21 using a light beam incident on the substrate 62 can be examined, so that the light beam 62 not through the sample 21 needs to reproduce. In another embodiment, the sensor is 50 not constructed as a dielectric mirror, but as an antireflection film stack. In this configuration, the light beam passes through 62 at non-resonance angles the sensor 50 essentially without diffusion or reflection and emerges as a light beam 64 out. That's how it works the dielectric film stack of the sensor 50 when formed as a dielectric antireflection film stack, directly opposite to the case where it is formed as a dielectric mirror. The configuration of the dielectric film stack, either as a dielectric mirror or as an antireflection film stack, will be explained in more detail below.

Regardless of whether the dielectric film stack is provided as a dielectric mirror or antireflection film stack, the dielectric film stack functions as a waveguide at the resonance angles, such that the reflected light beam 66 and the transmitted light beam 64 show strong anomalies. At the resonance angles energy from the light beam 62 to the dielectric layers 52 transmitted to the dielectric film stack, so that the dielectric layers 52 act together as a waveguide. When the dielectric layers 52 acting together as a waveguide, a finite part of the incident light beam is planted 62 continued within the dielectric film stack. When the dielectric film stack is formed as a dielectric mirror, the residual light that does not propagate within the dielectric film stack traverses the sensor 50 and enters as a ray of light 64 out, resulting in a strong attenuation of the reflected light 66 and a strong intensification of the transmitted light 64 is effected. However, when the dielectric film stack is formed as an antireflection film stack, the remaining light becomes a light beam 66 Reflected, creating a strong attenuation of the transmitted light 64 and a strong intensification of the reflected light 66 is effected.

A sensitizing layer 58 is outside the outermost dielectric layer 52 designed and for interacting with a predetermined chemical, biochemical or biological substance 18 in the sample 21 selected. If the target substance 18 with the sensitizing layer 58 connects, there is a shift in the resonance angle due to the change in the refractive index of the sensor 50 , A quantitative measure of the concentration of the target substance 18 can be determined by the magnitude of the shift of the resonance angle by monitoring either the reflected light 66 or the transmitted light 64 be calculated. Thus, there is an advantage of the sensor 50 compared to conventional SPR sensors in that the sensor 50 can be used in reflection-based scanning systems or in transmission-based scanning systems.

In one embodiment, the dielectric film stack is provided as a dielectric mirror by forming each dielectric layer with a dielectric material selected from a first dielectric material and a second dielectric material. The first dielectric material has a first refractive index while the second dielectric material has a second refractive index. In a particularly advantageous configuration, the stack of dielectric layers is formed such that the dielectric material of the dielectric layers alternates between the first dielectric material and the second dielectric material. For example, in one embodiment, the dielectric materials are the dielectric layers 52 selected such that the dielectric layers 52 ₁ and 52 ₃ have a high refractive index while the dielectric layer 52 ₂ has a low refractive index. This configuration is advantageous because the size of the anomalies of the light rays 64 and 66 are significantly and easily detectable, reducing the sensitivity of the sensor 50 is increased.

wobei λ die Wellenlänge des Lichtstrahls 62, n der Brechungsindex der dielektrischen Schicht, die ausgebildet wird, und m eine beliebige positive ganze Zahl ist. Für andere Auftreffwinkel ist diese Gleichung auf einfache Weise modifizierbar.When the light beam 62 the dielectric film stack of the sensor 50 penetrates, becomes part of the light beam 62 at each dielectric layer 52 reflected. In particular, when the light beam 62 a given dielectric layer 52 penetrates a portion of the light at the surface of the next dielectric layer 52 reflected. Thus, when the light beam 62 perpendicular to the dielectric film stack, the total distance traveled in a given dielectric layer is approximately twice the thickness t of the dielectric layer, ie 2t. For forming the dielectric film stack as a dielectric mirror, so that the light beam 62 from the sensor 50 essentially as a light beam 66 is reflected, each dielectric layer 52 formed with an approximate thickness t, which is defined by the following equation:

where λ is the wavelength of the light beam 62 , n is the refractive index of the dielectric layer that is formed, and m is an arbitrary positive integer. For other landing angles, this equation is easily modifiable.

If each dielectric layer according to the above Equation is formed, and m is zero, the in a given dielectric layer covered total distance λ / 2n. This corresponds to an "optical" total distance traveled by each dielectric layer half a wavelength of light, namely λ / 2, which is one Retardation of 180 ° corresponds.

At the reflection surface there is a further retardation by 180 ° when the continuous dielectric layer has a high refractive index n and the next dielectric layer a low index has. Therefore, at each of these high index / low index interfaces, the reflected light beam is experienced 66 a total retardation of 360 ° and reverses in phase with that part of the light beam 66 , which has been reflected from this surface, to the surface of the dielectric layer passed through 52 back. When the dielectric film stack is formed according to the above equation and the dielectric layers 52 alternate between high index and low index is the total internally reflected light beam 66 in phase, whereby a gain is produced, which leads to a considerable reflectivity. For example, in this configuration, the sensor 50 be formed such that at least 50% or even at least 90% of the light beam 62 is reflected. The dielectric film stack functions as a dielectric mirror when the dielectric layers are formed according to the above equation with any positive integer m. As m increases, the thickness t increases by λ, so that the "total optical" distance traveled in a dielectric layer increases by a full wavelength λ, resulting in amplification and considerable reflectivity of the light beam 62 leads.

In one embodiment, this is for a group of alternating dielectric layers, such. B. the dielectric layers 52 ₁ and 52 ₃ The material used has been chosen to have the highest refractive index of a dielectric material on the sensor 50 can be trained. For example, titanium oxide TiO _{2 is} a suitable dielectric material because it has a refractive index of about 2.5. For the other dielectric layers, such as. B. the dielectric layer 52 ₂ The material used is selected to have the lowest refractive index of a dielectric material on the sensor 50 can be trained. For example, silicon dioxide SiO _{2 is} a suitable dielectric material because it has a refractive index of about 1.5. Selecting the dielectric materials for the dielectric layers 52 At most angles, this results in a dielectric mirror with a high reflectivity, which often approaches 90%, but with strong attenuation at the resonance angles, which often approach 0% of reflected light. Further, a suitable dielectric material for the dielectric layer 52 ₂ have a corresponding refractive index approaching 1.8. Similarly, a suitable dielectric material for the dielectric layers 52 ₁ and 52 ₃ have a corresponding refraction angle of at least 2.2. Furthermore, the size of the anomaly shown increases with an increasing number of dielectric layers; however, the magnitude of the angular displacement tends to decrease. Therefore, a balance must be determined between these two characteristics. Although a different number of layers is acceptable, it has been found in experiments that five to fifteen dielectric layers give good results, with a number of eleven layers proving particularly good.

For using the dielectric film stack of the sensor 50 As a dielectric mirror, it is not necessary for the dielectric film stack to be formed of two alternating dielectric layers. A mirror made of dielectric layers may also be formed of dielectric layers having a plurality of different refractive indices. In this case, it is important that the thickness of each layer is determined by the above equation. Furthermore, each layer must be bounded by other layers, both of which have either a higher refractive index or a lower refractive index. By way of example, the dielectric film stack can be formed from three dielectric materials with indices n ₁ , n ₂ , n ₃ , where n ₁ <n ₂ <n ₃ . A suitable dielectric film stack made from these materials may be formed with the following sequence of dielectric indices: n ₃ , n ₂ , n ₃ , n ₁ , n ₂ , n ₁ , n ₃ , n ₂ , n ₃ .

As described above, the dielectric film stack of the sensor 50 be designed such that it acts as a dielectric antireflection film stack. Although no general equation is given for forming antireflection film stacks, an iterative approach using computational modeling may be used. According to this approach, an example of a dielectric antireflection film stack is TiO ₂ , SiO ₂ and TiO ₂ deposited on a glass substrate, wherein the refractive index of the TiO ₂ layers is 2.5 and the refractive index of the SiO ₂ layer and the glass substrate is 1.5 be. In this configuration, the thickness of the TiO ₂ layer on the substrate is 102 nm, the thickness of the SiO ₂ layer is 120 nm, and the thickness of the outer TiO ₂ layer is 114 nm. The strength of the reflected light for incident light perpendicular to the substrate at a wavelength of 635 nm is substantially zero.

4 shows an embodiment of a scanning system 100 with the improved optical sensor described above 50 , The scanning system 100 has a monochromatic light source 102 on, such as As a laser, the on a diffuser 105 incident light beam 24 generated. Other light sources are also suitable, including a monochromatic light-generating incandescent lamp, such as a light bulb. A mercury lamp, a filtered light emitting diode, a white light source coupled to a filter, etc. The diffuser 105 he produces a diffuse light beam 24 so the light 110 in a variety of angles on the sensor 50 incident. In one embodiment, the sample includes material for generating a diffused light beam that impacts the sensor such that no separate diffuser is needed. Depending on the angle of incidence and corresponding resonance angles of the sensor 50 becomes the light 110 through the sample 21 and the sensor 50 let through and illuminate a polarizer 114 , which is a polarized beam of light 117 with an electrical vector parallel or perpendicular to the grooves in the surface of the sensor 50 pass through.

A lens 115 focuses polarized light 117 to a corresponding point on a detector array 120 , In other words, the polarized light 117 enters the lens at a variety of angles 115 and is according to the angle on the detector array 120 focused. The detector array 120 Outputs a signal indicating the corresponding strengths of the detector array 120 indicating focused light. Based on the signal, a controller determines 122 one or more resonance angles and calculates a measure of the target substance in the sample. This configuration is particularly advantageous in that no moving parts are required. In one embodiment, the controller outputs 122 an audible alarm when the calculated measure of the target substance 18 exceeds a predetermined threshold. After completion of the scan, the sensor 50 disposed of or cleaned and reused.

It are several embodiments an optical inspection method and an optical inspection device been described. In one embodiment, it is of the present invention to an optical sensor with a dielectric Film stack comprising a plurality of dielectric layers. each Dielectric layer comprises a dielectric material, the of a first dielectric material having a first refractive index and a second dielectric material having a second refractive index. In one embodiment the dielectric film stack is formed such that the dielectric Material of the dielectric layers between the first dielectric Material and the second dielectric material alternated. Of the dielectric film stack is either as a dielectric mirror formed, in such a way that incident on the sensor Light is reflected from the sensor, or formed as an antireflection film stack, in such a way that incident on the light beam light propagated through the sensor.

Of the Sensor is easy to manufacture, so the resonance angle to simple Can be tuned, however, the diffraction grating based SPR sensors overcome limitations imposed become. In particular, the sensor uses a dielectric film stack a thin one Used metal foil. The sensor shows a resonance in its Size the resonances comparable to those normally encountered with conventional SPR sensors. Unlike with diffraction grating based SPR sensors However, a sample can be examined by reflection from the substrate side without the light propagating through the sample. Further allows it is the sensor that examines a sample with transmitted light. One The advantage of studying with transmitted light lies in the possibility a source for to use diffused light. Because the sensor is not on the use relied on conductive metals, the sensor also allows strong Resonances at shorter wavelength than traditional SPR sensors the case is.

Claims (12)

Sensor for optically examining a substance in a sample, comprising - a substrate ( 51 ) with a grooved surface ( 53 ), - one on the grooved surface ( 53 ) of the substrate ( 51 ) trained waveguides ( 52 ), and - one on a surface of the waveguide ( 52 ) relative to the substrate ( 51 ) sensitizing layer ( 58 ) for interacting with the substance ( 18 ), characterized in that the waveguide ( 52 ) - a dielectric film stack with a plurality of dielectric layers ( 52 ₁ . 52 ₂ . 52 ₃ ), wherein furthermore the thickness and the refractive index of each dielectric layer ( 52 ₁ . 52 ₂ . 52 ₃ ) are selected such that at least one angle of incidence of the dielectric film stack ( 52 ) as a waveguide for the sensor ( 50 ) incident light acts. Sensor according to claim 1, wherein at least two of the dielectric layers ( 52 ₁ . 52 ₂ . 52 ₃ ) comprise a dielectric material selected from a first dielectric material and a second dielectric material, the first dielectric material has a first refractive index n ₁ and the second dielectric material has a second refractive index n ₂ , and the dielectric film stack is formed such that the dielectric material the dielectric layers ( 52 ₁ . 52 ₂ . 52 ₃ ) alternates between the first dielectric material and the second dielectric material. Sensor according to Claim 1 or 2, in which the dielectric film stack ( 52 ) is formed as a dielectric mirror, so that on the sensor ( 50 ) is reflected by the sensor when the dielectric film stack is not as Waveguide acts. Sensor according to Claim 3, in which the dielectric film stack ( 52 ) such that, when the dielectric film stack functions as a waveguide, the reflected light has an attenuation of substantially at least 50%. Sensor according to Claim 1 or 2, in which the dielectric film stack ( 52 ) is formed as an antireflection film stack, so that the incident light the sensor ( 50 ) passes through when the dielectric film stack ( 52 ) does not function as a waveguide, and the transmitted light has an attenuation of substantially at least 50% when the dielectric film stack ( 52 ) acts as a waveguide. A sensor according to claim 2, wherein the first refractive index n ₁ is substantially not greater than 1.8 and further the second refractive index n ₂ is substantially not less than 2.2. Sensor according to claim 2, wherein the first dielectric Material silicon dioxide and the second dielectric material titanium dioxide is. Scanning system for optically examining a substance in a sample, comprising - a light-generating light source ( 102 ), - a sensor ( 50 ) according to one of claims 1 to 7, - a detector ( 120 ), the light from the sensor ( 50 ) and generates an output signal depending on the light intensity, and - one with the detector ( 120 ) coupled controllers ( 122 ) for calculating a measure of the substance ( 18 ) in the sample ( 21 ) in response to the output signal. Scanning system according to Claim 8, in which the light source ( 102 ) a diffuser ( 105 ) for generating one on the sensor ( 50 ) incident diffuse light beam, the scanning system further comprising a polarizer ( 114 ) for polarizing the detector ( 120 ) receiving light, and wherein the light source ( 102 ) is a monochromatic light source. Method for examining a sample, comprising the following steps - allowing a sensor to interact ( 50 ) according to one of claims 1 to 7 with a sample ( 21 ) with a target substance ( 18 ), and - determining a measure of the target substance ( 18 ) in the sample ( 21 ) in response to a detected optical anomaly of the sensor ( 50 ) coming light. The method of claim 10, wherein determining the measure comprises detecting an optical anomaly in the sensor. 50 ) comprises reflected or transmitted light. The method of claim 10, wherein determining the measure includes illuminating the sensor. 50 ) with diffused light ( 110 ) and detecting an optical anomaly in the sensor ( 50 ) transmitted light by focusing the transmitted light on a detector array ( 120 ) corresponding to a transmission angle of the transmitted light.